Electron beam tube



y 29, 1956 I J. R. PERILHOU ETAL 2,748,313

ELECTRON BEAM TUBE Filed April 10, 1952 2 Sheets-Sheet l J13 10y b J6INVENTORS Jeun Robert Perilhou Johan Lodewijk Hendrik Jonker AGE/VT y29, 1956 J. R. PERILHOU ET AL 2,748,313

ELECTRON BEAM TUBE Filed April 10, 1952 2 Sheets-Sheet 2 INVENTORS JeunRobert Perilhou Johan Lodewijk Hendrik Jonker BY %W@% AGENT 2,748,313Patented May 29, 19.

ELECTRON BEAM TUBE Jean Robert Perilhou and Johan Lodewijk HendrikJonker, Eindhoven, Netherlands, assignors to Hartford National Bank andTrust Company, Hartford, Conn., as trustee Application April 10, 1952,Serial No. 281,612

Claims priority, application Netherlands May 2, 1951 6 Claims. (Cl.315-25) This invention relates to devices comprising an electron beamtube having an electrode system comprising at least a cathode, anaccelerating anode, a collecting electrode and a grid provided betweenthe accelerating anode and the collecting electrode. It furthermorerelates to electron beam tubes for use in such devices.

There are in principle two kinds of electron tubes, viz. firstly tubesin which the electrons after leaving the oathode are subject toelectrostatic or electromagnetic forces such that the electrons areunited to form a beam, and secondly tubes in which such a beam does notoccur. The present invention relates to the first-mentioned kind oftubes and to devices comprising such tubes. They include inter aliacathode-ray tubes for oscillography or television purposes and alsotubes by which electrical oscillations are produced, amplified,rectified or influenced in other manner. The invention is of general usein such kind of tubes and relates more particularly to the manner inwhich the electron beam is controlled. Two methods of control may beused in electron beamtubes. The first is similar to the control whichmay also be used in tubes in which the electron current is not formedinto a beam; as a rule, it is referred to as intensity control. In thesecond method of control, socalled deflection control, the whole of theelectron beam is deflected in some direction or other. The intensitycontrol is, as a rule, brought about by an electrode in grid form whichtransmits a greater or smaller portion of the electron current. In manycases, for example in oscillography or television tubes, this grid hasthe shape of a plate having a small aperture.

In deflection control use is made of an electrostatic or electromagnetictransverse field.

Since the invention uses deflection control by means of a grid-likeelectrode, the explanation following hereinafter is necessary forcorrect understanding of the invention.

It is known that a grid provided between a cathode and an anode and towhich a positive voltage with respect to the cathode is applied exerts acertain concentrating action upon an electron current. In passing such agrid, the electron current is divided into a plurality of narrow beams,the number of which corresponds to the number of meshes of the part ofthe grid covered by the electron current. Said narrow beams may beconvergent or divergent, according to the charge on the grid. The chargeon the grid is determined by the potential applied and by the positionof the grid in the potential field between the cathode and thecollecting electrode or anode. If the potential of the grid is lowerthan the potential which would prevail at the area of the grid in theabsence thereof, the grid assumes a negative charge. In this case thebeams after the grid are convergent. Consequently, as viewed from thecathode, there are beyond the grid a series of focal points which may belocated before, on or after the anode.

The above-mentioned phenomenon naturally also occurs if the electroncurrent passing to the grid is already united into a beam. This beamingneed not necessarily be understood to mean that all of the electronsextend in parallel paths, but that there is a distinct main direction ofthe electron current. If the electron beam before the grid is wide withrespect to the width of the meshes of the grid, a plurality ofconvergent beams occur after the grid, if this has a negative charge,which beams are each narrower than the initial beam. If the initialwidth of the beam is equal to or smaller than the width of the meshes, aconcentrating action is exerted upon such a beam by the grid withnegative charge, so that a focus may be produced which may be locatedbefore, on or after the collecting electrode.

The phenomenon underlying the invention is the following. When anelectron beam after passing a grid having applied to it a positivevoltage enters an electrostatic field between the grid and collectingelectrode in which the direction of the lines of force intersects thedirection of the incident beam, deflection of the electron beam takesplace, which is dependent inter alia upon the difference in potentialbetween the grid and the collecting electrode.

If the grid is negatively charged by the arrangement with respect tocathode and anode, then of course, the above-described concentrationoccurs in addition to the deflection.

A device according to the invention comprises an electron beam tubehaving an electrode system comprising at least a cathode, anaccelerating anode, a collecting electrode and a grid provided betweenthe accelerating anode and the collecting electrode and having appliedto it apotential higher than that of the cathode and lower than that ofthe collecting electrode. The collecting electrode and the grid are sopositioned that the direction of the electron beam just before the gridintersects the lines of force between the grid and the collectingelectrode, whilst furthermore, an alternating control voltage, withrespect to the collecting electrode is set up at the, grid which resultsin a varying deflection of the electron. beam between the grid and thecollecting electrode being v obtained.

It is evident that, as a rule, an electron beam tube re-. quires the useof more electrodes for producing a beam than the above-mentionedelectrodes. Since the inven-- tion is independent of the manner in whichthe beam is produced, the simplest system for producing a beam is givenin the description following hereinafter and in the claims. However, anysuitable means for producing a beam, either divergent or convergent, canbe used in an electron beam tube and a device according to theinvention.

In a device according to the invention, the beam in the discharge tubemay furthermore be controlled by other means than by the grid providedbetween the collecting electrode and the accelerating anode. Thus, forexample, the intensity of the beam may be varied by means of a diaphragmor a so-called Wehnelt cylinder. The beam may also be deflected in anelectrostatic or electromagnetic manner before reaching the grid(hereinafter referred to as the deflection grid) provided between thecollecting electrode and the accelerating anode.

The invention increases the number of possibilities for acting upon thebeam, of which an advantageous use may' be made for many purposes, sinceapart from the re quirements for obtaining the above-mentioneddeflection by the grid, there are no restrictions with regard to thestructure of the electrode system. Consequently, use may' be made, forexample, of grids comprising solely parallel' wires or grids comprisingcrossing wires. The simplest form of the grid is constituted by twoparallel wires between which the electron beam passes. Furthermore, a

plurality of control methods may be used in combina tion.

The direction of the deflection brought about by the deflection grid ina tube in which deflection is also used before said grid may coincidewith this direction or differ therefrom, for example it may be at rightangles thereto. In the former case the deflection grid permits, forexample, of providing a correction of the deflection already produced.

, In tubes in which the beam is deflected before the deflection grid,the angles of the beam in its various positions with respect to the gridare in most cases different. However, the deflection brought about bythe grid is inter alia dependent upon the said angles. If it is desired,on account of a given variation in potential of the grid, to bring abouton the collecting electrode a shift of the striking point of the beam onthe collector which is independent of the angle made by the incidentdeflected beam with the grid, it .is necessary to take particular steps.

For this purpose, for example, the grid electrode and, if necessary, thecollecting electrode may be given a predetermined curvature. For planeelectrodes there is a different solution, since if the deflection gridand the collecting electrode are located in different planes, theenvisaged object is attained if said planes are at an angle to oneanother such that the direction of each electron beam just beforereaching the grid makes, with the grid surface at this area, an anglewhich is more acute than that made with the plane of the collectingelectrode.

If in a tube in which deflection takes place before the deflection grid,this grid has an even width of meshes or pitch, it is unavoidable thatthe angle enclosed by two lines passing through the centre of rotationof the swinging beam and two adjacent grid wires is different fordifferent positions of the grid. 'The beam, so to say, views the gridmeshes from the centre of rotation at a different angle, resulting in adifference in intensity of the focal spot behind each mesh of the grid.

Said difference may be obviated if the spacing between every twoadjacent grid wires is made smaller, according as the direction of theelectron beam just before the grid encloses a larger angle with theplane of the grid at the area at which the beam passes through it.

It is evident that the above-mentioned steps may be used in combination.

As a rule, it suifices if the voltage supplied and the position of thedeflection grid are such that the beam upon reaching the grid isconcentrated by the grid so that the width of the beam, measured atright angles to the direction of the grid wires, at the area at whichthe beam strikes the collecting electrode, is at the most equal to halfthe width of the beam at the moment at which the beam reaches the grid.

It will have appeared from the aforegoing description that the spacingbetween the deflection grid and the collecting electrode acts upon boththe concentrating action of the grid and its deflecting action. As arule, the smallest spacing between the grid and the accelerating anodeis larger than the smallest spacing between the grid and the collectingelectrode.

As explained above, it is necessary that an electrostatic field may bebuilt up between the deflection grid and the collecting electrode. Ifthe collecting electrode consists of metal, difficulties are not to befeared, However, if the collecting electrode is a luminescent screen,steps must be taken to build up said field. For example, it is possiblein known manner to mix the luminescent substance with conductivematerial, for example metal. As an alternative, that side of theluminescent screen which is adjacent the cathode may be covered with ametal layer permeable to electrons (so-called metal backing). Anothersolution consists in providing a grid before or after the luminescentscreen, which grid fulfils the function of the collecting electrode, butwhich does not prevent the electrons from striking the luminescentscreen. For carrying off the charge then acquired by the screen, one hasto have recourse to means already known for avoiding said charge,consisting inter alia in a sufficient secondary emission of the screen.The secondary electrons may in this case be collected by the grid-likecollecting electrode.

In order that the invention may readily be carried into effect, a numberof examples will now be described in detail with reference to theaccompanying drawings, of which:

Fig. 1 shows diagrammatically the manner in which the electron beam isdeflected;

Figs. 2, 3 and 4 are other embodiments of the system shown in Fig. 1;

Figs. 5, 6 and 7 show diagrammatically an electron beam tube with thenecessary connections for the electrodes, together with a source ofsupply.

In Fig. l, the reference numeral 1 indicates a cathode, emittingelectrons which are united to form a beam by means which are not shown.2 is the collecting electrode and 3 the deflection grid provided infront of it. The electrode 2 has applied to it a potential higher thanthat at the grid 3, which in turn has a potential higher than that ofthe cathode 1. The lines of force between the electrodes 2 and 3 extendin accordance with the lines designated 4. The beam indicated by 5passes through the grid in a direction such that the direction of thelines of force 4 is intersected. Since the electrons after the grid havea tendency to follow the lines of force, a curved path ensues asindicated by 6. It is to be noted that naturally the beam has aparticular cross-section, which is not shown for the sake of simplicity.If the grid 3 has a negative charge, the curved path 6 is convergent.This may be of importance if, for example, a sharp focus on thecollecting electrode 2 is desired,

The operation of a device according to the invention is based on thefact that an alternating control-voltage is set up between the grid 3and the electrode 2, so that the field gradient between the grid 3 andthe collecting electrode 2 varies. This will also result in variation ofthe curvature of the path 6, so that the beam strikes the electrode 2 atanother point.

Since the operation is based on the fact that the direction of theelectron beam before the grid intersects the direction of the lines offorce between the grid and the collecting electrode, it will be evidentthat there is one casein which deflection cannot occur at all, viz. ifboth grid and collecting electrode are at right angles to the directionof the beam. However, either of the electrodes 2 and 3 may be at rightangles to the beam. An example in which the grid is at right angles tothe beam is shown in Fig. 2, in which identical elements bear the samereference numerals as in Fig. 1. It is evident that in this case thelines of force extend according to curved paths.

In Figs. 1 and 2 there was no question of deflection of the beam 5before the grid 3. As explained before, irregularities occur if the beam5 is deflected over the grid 3. The irregularities are due to the factthat the beam which shifts to and fro over the grid, from the centre ofrotation, views the apertures between the grid wires at differentangles. Fig. 3 shows an arrangement of the electrodes in which grid 7has a pitch which regularly decreases from one end to the other. Theelectron beam 9 is deflected by deflection-plates 10 and 11, shifting toand fro over the surface of the grid 7. If 12 indicates the centre ofrotation of the electron beam, the spacing between the grid Wires issuch that the angles a and b are equal. The collecting electrode in thisfigure is indicated by 13.

In Fig. 4, the grid and the collecting electrode are designated 14 and15 respectively. In this construction it is assumed that the beam turnsabout a point 16. 1f the grid 14 were parallel to the collectingelectrode 15, the deflection brought about by the grid would be greaterat the upper end than at the lower end. Consequently, the shift of thestriking point of the beam on the collecting electrode 15 for the samevariation in potential of the grid 14 would be larger at the upper endof the collecting electrode 15 than at the lower end. The difference indeflection and hence in shift of the striking point is due to the moreacute angle which the electron beam in this case would enclose with thegrid at the upper end of the grid, since the more acute this angle, thegreater is the deflection. If the grid is positioned at an angle to thecollecting electrode, as shown in the figure, the length of the electronpaths between the electrodes 14 and 15 is at the upper end of the gridsmaller than at the lower end. Consequently, with a suitable arrangementit may be ensured that the shift of the striking point on the collectingelectrode 15 for the same variation in potential between the electrodes14 and 15 is the same throughout.

Fig. shows diagrammatically one form of construction of a deviceaccording to the invention with the associated connections and a sourceof supply. An electron beam tube 17 comprises a system (shown here ingreatly simplified form) for producing, concentrating and deflecting theelectron current emitted by a cathode 18. The cathode 18 is heated by afilament 19 to emit an electron current concentrated inter alia by anaccelerating anode 20 to form a beam. The electron beam may be deflectedby means of a set of deflection plates 21 and 22 and is deflected over agrid 23, which is equivalent to the grids 3, 7 and 14 from Figs. 1, 2, 3and 4. Behind grid 23 is a collecting electrode 24, which may be coatedwith luminescent material. The various voltages for the electrodes arederived from a potentiometer 25, which is connected to a source ofsupply 26. The alternating voltages bringing about the deflection of theelectron beam between the grid 23 and the collecting electrode 24 aresupplied by way of a transformer 27.

Fig. 6 shows a particularly simple form of construction of a deviceaccording to the invention, suitable for push-pull amplification ofelectrical oscillations. The general structure of the discharge tube isquite similar to that of Fig. 5 except for the deflection electrodes,since in a tube as shown in Fig. 6 the beam is not deflected between theaccelerating anode 28 and the grid 29. The latter comprises only twowires, the beam bedirected into the centre space between said wires.Behind the grid is the collecting electrode which is constituted by twoparts, viz. 30 and 31. When alternating voltages are supplied to thegrid 29 by way of a transformer 32, the beam may be directed alternatelyonto the electrode 30 and 31. Consequently, in this case also theoperation is similar to that of the deflection plates as used inconventional cathode-ray tubes. The great difference is, however, thatthere is only one electrode with only one voltage which brings about thedefiection.

Fig. 7 shows a device which is substantially identical with that shownin Fig. 6, except that here, so to say, a multiple collecting system isprovided. The electrons in this case travel after an accelerating anode33 in the form of a divergent beam, which is divided by a grid 34 into aplurality of narrower beams 35 which move according to curved pathstowards a collecting electrode 36. The collecting electrode 36 issubdivided into a plurality of small electrodes which are alternatelyconnected to another. In supplying an alternating voltage to the grid 34it may be ensured that all of the beams 35 simultaneously strike onegroup of electrodes or the other group of the electrode 36.Consequently, there is push-pull action similarly as in Fig. 6. Thegreat advantage is, however, that the beam is divergent and hence,capable of controlling a considerable amount of electricity.Consequently, the effect of this device is very great.

It will be clear that greatly difierent electrical phenomena may beproduced or acted upon in numerous ways with a device according to theinvention. Thus, for example, a device as shown in Figs. 6 and 7 permitsof producing oscillations in a simple manner by providing a couplingbetween the output electrodes and the grid.

The invention is thus not limited to the embodiments shown.

What we claim is:

l. A circuit-arrangement comprising a cathode-ray tube including acathode for producing electrons, means including an accelerating anodefor forming said electrons into an electron beam, a planar collectorelectrode positioned in the path of said electron beam, a planar gridelectrode positioned in the path of said electron beam between saidcollector electrode and said anode, the planes of said collectorelectrode and grid electrode being oblique to the path of said electronbeam, means connected to apply to said collector electrode apositivepolarity potential with respect to said cathode whereby avoltage field is produced which has a finite value in the region of saidgrid electrode, means connected to apply to said grid electrode apotential intermediate the potentials of said cathode and collectorelectrode and having a value which is negative with respect to saidfinite value whereby said grid assumes a negative charge thereby tocause said electron beam to converge as it approaches said collectorelectrode, and a source of alternating voltage connected to said gridelectrode to produce a varying deflection of said beam with respect tosaid collector electrode, said grid electrode being substantiallycompletely transmissive for said electron beam so that substantially allof said electron beam passes through said grid electrode at all timesand impinges upon said collector electrode.

2. A circuit-arrangement as claimed in claim 1, in which said collectorelectrode comprises a coating which luminesces in response toimpingement by said electron beam, and including a beam deflecting meanspositioned to deflect said electron beam before it reaches said gridelectrode.

3. A circuit-arrangement as claimed in claim 2, in which the planes ofsaid collector electrode and said grid electrode are positioned at anangle with respect to each other, whereby the amount of deflection ofsaid electron beam due to said alternating grid voltage is substantiallyuniform throughout the surface of said collector electrode.

4. A circuit-arrangement as claimed in claim 3 in which said gridelectrode comprises a plurality of mutually parallel wires.

5. A circuit-arrangement as claimed in claim 4, in which the spacingbetween adjacent grid wires is successively larger toward the edge ofthe grid which is farthest from the source of said electron beam.

6. A circuit-arrangement as claimed in claim 5, in which the potentialapplied to said grid electrode is adjusted to a value to cause saidelectron beam to converge to a width at said collector electrode ofsubstantially onehalf of the width of said electron beam at said gridelectrode.

References Cited in the file of this patent UNITED STATES PATENTS2,071,382 Balsley Feb. 23, 1937 2,136,105 Jobst Nov. 8, 1938 2,144,085Rothe et a1 Jan. 17, 1939 2,201,587 Krawinkel May 21, 1940 2,212,645Morton Aug. 27, 1940 2,401,740 Kilgore Jan. 11, 1946 2,463,535 Hecht May8, 1949 2,529,408 Montani Nov. 7, 1950 2,570,790 Gray Oct. 9, 19512,577,038 Rose Dec. 4, 1951

